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Tuesday, November 6. 2007

I spent a fair few hours last month fixing problems on relatives PCs. It's always the way, isn't it? Once people know 'you work with computers', you become a PC expert!

Anyway, one of the trickier problems was with my old (well, only about 14 months old) laptop that I've passed over to Mads. Performance was atrocious and I was surprised because I'd reinstalled XP to give it a spring clean. At first performance wasn't *too* bad, but it got worse and worse and was particularly bad when the anti-virus software kicked in. As far as I could see (and I mean *see*) the hard drive was churning away and I originally thought there might a problem with Spyware (there was) memory (it's only got 512MB) but there was something more. It was awful.

One night Mads had had enough and so I was determined to do something about it (I promise she didn't threaten me). I ran some online checks at PC Pitstop and it highlighted the following :-

Drive C has an uncached speed of 2 megabytes per second.

For comparison, systems with the same CPU and clock speed as this one have a speed of 19.33 MB/s

Make sure DMA is enabled on all disk drives. Not using DMA mode can cause a significant reduction in disk speed.

When I check the Primary IDE interface's Advanced Settings in Device Manager, I noticed that the Transfer Mode was set to "DMA if available" but that the Current Transfer Mode was set to "PIO". After a bit of investigation, this note from Microsoft looked promising so I followed the instructions. Sure enough, it's been using "Ultra DMA Mode 5" since then and the improvement is dramatic. The uncached speed increased to 6 MB/s which is still poor but sufficient. It's been running for several weeks now without being downgraded to PIO mode.

Like those who reboot servers unneccesarily because of some performance problem they hit years ago, I suspect I'll be checking the Current Transfer Mode on poorly-performing PCs for some time to come

It's a minor source of frustration to me that you can't just paste a Hypertext link into the comments form here but, should you ever want to include a link, all you need to do is use the BBCode format, as mentioned below the comment form.

Here is a link to the relevant part of the document that explains how.